A sensor device produces an output signal in response to a specified measurement. There are terms which are often used synonymously for sensors, such as transducers and detectors. A transducer is more generally defined as a device which converts energy from one form to another. An output signal refers to an optical, electronic or mechanical signal. There are many different kinds of sensors, such as mechanical, electrical, magnetic or chemical sensors. Active sensors use an input power to accomplish transduction. Some sensors employ multiple transduction mechanisms in order to produce an electronic output signal in response to the measurement. The sensor detects the state or condition of some underlying system and transmits information about said state to some higher level entity.
As the implementation of processors has become cheaper, it is now possible to package the sensor hardware with a micro-processor and a transceiver into a single device. Accordingly, sensors can comprise a sophisticated programmable logic. This allows, for example, determining under which circumstances the sensor is read and which information is transmitted.
Previously-proposed low end sensor units are typically battery-powered allowing them to execute a measurement in environments where cabling would be unfeasible or prohibitively expensive. Previously-proposed protocols and software that runs on such sensors are designed for the reduced power consumption of such sensors in order that the batteries of the sensors have to be replaced with reduced frequency. In particular, as the radio power varies with the square of distance, such sensors form typically a network where messages from sensors are forwarded across other sensors to reach a destination device processing these sensor data. Accordingly, the radio or transceiver unit of such a sensor constantly draws power from the power source of the sensor, even when the sensor is idling.
Consequently, in a previously-proposed energy efficient network, the data communication protocols are designed to allow the transceiver of the sensor to be put to sleep as often as possible.
However, a disadvantage of such sensor networks resides in that, when the sensor only rarely sends sensor data to the processing unit the processed sensor data is outdated so that the system does not react to the actual state of the environment.
Accordingly, it is desirable to provide a method for reducing the power consumption of sensors within a sensor network and preserving integrity of the sensor network at the same time.